Phenethylammonium Halide Blend as an Efficient Interlayer in Solution-Processed Inverted Planar <i>p</i>–<i>i</i>–<i>n</i> Perovskite Solar Cells

Inverted planar (p–i–n) perovskite solar cells (PSCs) are gaining popularity due to their low-temperature processability, excellent device stability, flexibility, and negligible J–V hysteresis. In solution-processed p–i–n PSCs, the interface between the HTL (hole transport layer) and the perovskite absorber is vital in determining the device performance. To improve this interface, currently, the approaches involve expensive materials and complex processing methods. Herein, we introduce a blend of two alkylammonium halides, phenethylammonium iodide (PEAI) and phenethylammonium bromide (PEABr), as an interlayer on top of the Spiro-based HTL in p–i–n PSCs with a cost-effective approach, which significantly improves the interface quality, wettability (improving the hydrophilicity), and energy alignment, resulting in improved photovoltaic device performance. An optimized ratio of PEAI to PEABr results in optimized device performance having a power conversion efficiency (PCE) greater than 18% with a short-circuit current density (JSC) of 22.71 mA cm–2, an open-circuit voltage (VOC) of 1.09 V, and a fill factor (FF) of 74.78%. In comparison to devices using a polymeric interlayer (PFN-P1), the phenethylammonium halide blend interlayer-based devices offer comparable efficiency at a much lower cost and with a simpler fabrication process. Moreover, it avoids the need for an ultrathin layer formation. Thermal stability tests demonstrate that devices with the phenethylammonium halide blend interlayer retain over 80% of their initial efficiencies after more than 700 h of thermal aging at 85 °C, showing better durability compared to PFN-P1 polymer interlayer-based devices.